Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Des Moines Iowa
625 PM CDT Wednesday Apr 23 2014
Short term /tonight/...
issued at 313 PM CDT Wednesday Apr 23 2014
Ongoing precipitation across central Iowa will continue to push
eastward. May see lingering scatter showers with isolated
thunderstorms in the south and east for the early evening hours.
Winds will continue to be strong and gusty...however...will begin to
diminish slightly as low pressure system approaches. Will keep Wind
Advisory for northwestern County Warning Area...with sustained winds near advisory
criteria. However...anticipate it will be allowed to expire on time.
Next concern becomes precipitation chances overnight. Low pressure
system will push eastward...with increasing precipitation chances.
Models are a bit slower...and given current lack of precipitation in
central NE will keep a slightly slower solution.
However...anticipate late afternoon/early evening convection to
develop in Nebraska which will push east with low. In
addition...good swath of Theta-E advection will help keep
precipitation going into Iowa especially as low level jet increases overnight.
A few thunderstorms may be strong to severe with decent instability
and good shear. However...main concern will be with precipitation
with strong moisture flow into system. Soundings indicate precipitable water
values near or above 1 inch...which is seasonally high. Therefore
some thunderstorms may produce locally heavy rainfall.
Long term /Thursday through Wednesday/...
issued at 313 PM CDT Wednesday Apr 23 2014
The extended can be characterized by two words...wet and cold. For
tomorrow the surface low and frontal boundary will push east
through early afternoon. The instability will push east with it
but the upper level short wave will lag behind and take most of
the rest of Thursday to clear the area. Thus we will see showers
continuing through most of the day and thunderstorms in the
morning. The storms become isolated by late morning/early
afternoon and will be mainly confined to eastern Iowa in the
afternoon. Clearing from west to east late in the day. An
additional four to six tenths of an inch of rainfall is
expected...mainly over the east so most locations will get a good
soaking by Thursday afternoon.
Ridging will build into into the plains Thursday night through
Saturday but Iowa will remain in a west to northwest flow aloft.
We will warm nicely on Friday with highs back in the 60s and 70s.
Beyond Saturday the forecast is still uncertain as far as temperatures
and just how the western low/trough will develop. The GFS has been
consistent in deepening the low over The Four Corners area which
will sharpen the ridge over the upper Midwest. At the surface a
low will develop over NE Colorado/western NE with a warm front stretching
into northwest MO...possibly into SW Iowa. The location of the front will
be key to what will happen in Iowa. The Euro has been all over the
place with the evolution of the upper feature...bouncing between
The Four Corners area to Colorado. The latest run is back to the
south and similar to the GFS again. As the upper low migrates east
it will tap the Gulf and there will be strong moisture advection
into the state the frontal boundary at this point looks to remain
just south of the forecast area but good overrunning will bring
thunderstorms into at least southwest portions of the state but
the severe threat should be just to our south. Still concerned
with heavy rainfall though. If we were to get stronger storms the
period of concern at this point would be Sunday afternoon/evening
but there are too many details that still need to be resolved
before pinning down a time.
The model consensus at this point...unless the Euro changes yet
again...is for the upper Midwest to be on the cold side of this
storm system but temperatures are not as cold as were depicted a couple
days ago. Therefore ptype is all rain but the threshold is narrow
so if we can get a little colder air drawn down there still may be
a mix across the very far north. At this point however I have just
rain in the forecast. The cool and wet pattern will persist into
early next week with highs only in the 50s.
issued at 622 PM CDT Wednesday Apr 23 2014
Southeasterly flow of moist air ahead of cold front will result in
deteriorating conditions in ceilings and thunderstorms and rain. Showers this evening
will give way to widespread thunderstorm activity before midnight
in the west and over the County Warning Area overnight. MVFR ceilings with showers on
Thursday. Conditions will improve over the western taf sites
during the afternoon and remain MVFR over the east.
Outlook...clouds will clearly rapidly Thursday evening with good VFR
conditions expected for Friday into Friday night.
aviation...MS Apr 14